Can sombody help me with this please

If we declared a static variable inside a procedure called sum, what would be the sum when we run this procedure the third time if var=5 and sum=0; Note: the initial value of var = 5?

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

Dim var1 As Integer

Static sum As Integer

Integer.TryParse(TextBox1.Text, var1)

sum = sum + var1

Label1.Text = sum.ToString("n")

End Sub

What is the three-character extension appended to solution files in Visual Basic 2015?